There used to be known a conventional low height transformer, as shown in FIG. 16. In the conventional low height transformer, a core assembly 1 is formed by combining a pair of E-shaped cores 11, 12, and a primary coil N1 and a secondary coil N2 are wound within the core assembly 1. In the core assembly 1, end surfaces of side leg portions 1a, 1b of the respective E-shaped cores 11, 12 are opposed and are in contact with each other, respectively, while a gap G for inductance adjustment is provided between end surfaces of mutually opposing central leg portions 1c. The primary coil N1 and the secondary coil N2 are wound around a perimeter of the central leg portion 1c, using spaces between the central leg portion 1c and the side leg portions 1a, 1b as coil housing spaces.
In this type of low height transformer, due to limitations on coil winding space, the secondary coil N2, which has a small number of windings and outputs a low voltage and a large current, is formed of a strip-shaped rectangular wire wound by edgewise winding as shown in FIG. 17 (for example, refer to Japanese Patent Application Publication No. H10-22131).
In the conventional transformer, the primary coil N1 is wound in a region opposing a side face of the central leg portion 1c of the E-shaped core 11 (or 12) and the secondary coil N2 is wound in a region opposing the gap G. Therefore, the secondary coil N2 is wound such that an inner peripheral surface thereof contacts with the gap G. As a result, leakage flux from the gap G is to cross the secondary coil N2 composed of the rectangular wire, and causing an increase in eddy current loss.